Title:                           Theoretical Exploration of Mechanisms for the Formation of a Yellow ‘Polymer’ Residue During Phosphine Fumigation

Author:                       Stephen L. Garrison

Advisor:                      Carlos Gonzalez

Division:                     Physical and Chemical Properties Division

Laboratory:                Chemical Science and Technology Laboratory

Room:                         Building 221, Room B348

Mail Stop:                  8380

Telephone:                 301-975-4489

FAX:                           301-869-4020

E-mail:                        stephen.garrison@nist.gov

Sigma Xi Member?    No

Category:                   Chemistry

 

 

During fumigation with phosphine (PH3), a yellow residue, possibly a polyphosphide, has been sometimes been found. Previous and current work indicates that this unknown solid substance results from the reaction of phosphine (PH3) with nitric oxide (NO).

 

Using Density Functional Theory (DFT) methods we obtained clues to the polymer formation mechanism. The likely pathway begins with the reaction of PH3 and the NO dimer, a mild oxidant, leading to phosphine oxide (H3P=O) and nitrous oxide (N2O), followed by fast reorganization to a more stable intermediate, H2POH. Finally, a condensation reaction of H2POH with phosphorus compounds present, e.g., PxHy and PxHy(OH)z, results in the formation of the phosphorus hydride polymer.

 

The application of computational methods has helped provide a better understanding of the reaction mechanism allowing us to guide experimental studies on how to control the polymerization reaction. If the oxidant NO is removed from the system, possibly through the use of strong reductants, such as ascorbic acid or metal powders, formation of the residue might be suppressed.